Methods and systems for controlling an air conditioning system operating in free cooling mode

ABSTRACT

A method of controlling an air conditioning system having a cooling mode and a free-cooling mode, including activating the air conditioning system; measuring a first temperature of ambient air surrounding a condenser, measuring a second temperature of the working fluid; calculating a difference between the first and second temperatures; and comparing the difference to a predetermined value, wherein if the difference is greater than or equal to the predetermined value the free-cooling mode is activated, and wherein if the difference is less than the predetermined value the cooling mode is activated.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure is related to air conditioning systems. Moreparticularly, the present disclosure is related to methods and systemsfor controlling air conditioning systems having a free-cooling mode anda cooling mode.

2. Description of Related Art

During the typical operation of air conditioning systems, the airconditioning system is run in a cooling mode wherein energy is expendedby operating a compressor to compress and circulate a refrigerant tochill or condition a working fluid, such as air or other secondary loopfluid (e.g., water or glycol), in a known manner. The conditionedworking fluid can then be used in a refrigerator, a freezer, a building,a car, and other spaces with climate controlled environment.

However, when the outside ambient temperature is low, there exists thepossibility that the outside ambient air itself may be utilized toprovide cooling to the working fluid without engaging the compressor.When the outside ambient air is used by an air conditioning system tocondition the working fluid, the system is referred to as operating in afree cooling mode. As noted above, traditionally, even when the ambientoutside air temperature is low, the air conditioning system is run inthe cooling mode. Running in cooling mode under such conditions providesa low efficiency means of conditioning the working fluid. In contrast,running the air conditioning system under such conditions in a freecooling mode is more efficient. In the free cooling mode, one or moreventilated heat exchangers and pumps are activated so that therefrigerant circulating throughout the air conditioning system is cooledby the outside ambient air and then the cooled refrigerant is used tocool the working fluid.

Accordingly, it has been determined by the present disclosure that thereis a need for methods and systems that improve the efficiency of airconditioning systems having a free cooling mode.

BRIEF SUMMARY OF THE INVENTION

A method of controlling an air conditioning system having a cooling modeand a free-cooling mode is provided.

The method includes activating the air conditioning system; measuring afirst temperature of ambient air surrounding a condenser; measuring asecond temperature of a working fluid; calculating a difference betweenthe first and second temperatures; and comparing the difference to apredetermined value, wherein if the difference is greater than or equalto the predetermined value, the free-cooling mode is activated, andwherein if the difference is less than the predetermined value thecooling mode is activated.

An air conditioning system having a cooling mode and a free cooling modeis provided.

The air conditioning system includes a condenser; a first temperaturesensor for measuring a first temperature of ambient air surrounding thecondenser; a working fluid; an evaporator for housing a section of theworking fluid; an expansion valve being located before the evaporator; asecond temperature sensor for measuring a second temperature of theworking fluid; a controller for calculating a difference between thefirst and second temperatures, the controller comparing the differenceto a predetermined value, the controller activating the free coolingmode when the difference is equal to or greater than the predeterminedvalue, the device activating the cooling mode when the difference isless than the predetermined value; a refrigerant pump for pumpingrefrigerant from the condenser through an expansion valve to theevaporator when the air conditioning system is in the free cooling mode;a first valve for fluidly connecting the condenser to the expansionvalve when the air conditioning system is in the cooling mode, the firstvalve for fluidly connecting the condenser to the refrigerant pump whenthe air conditioning system is in the free cooling mode; a compressorfor compressing the refrigerant when the air conditioning system is inthe cooling mode; and a second valve for fluidly connecting theevaporator to the condenser when the air conditioning system is in freecooling mode, the second valve for fluidly connecting the evaporator tothe condenser when the air conditioning system is in the cooling mode.

The above-described and other features and advantages of the presentdisclosure will be appreciated and understood by those skilled in theart from the following detailed description, drawings, and appendedclaims.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is an exemplary embodiment of an air conditioning system incooling mode according to the present disclosure.

FIG. 2 is an exemplary embodiment of an air conditioning system in freecooling mode according to the present disclosure.

FIG. 3 illustrates an exemplary embodiment of a method according to thepresent disclosure of operating an air conditioning system having afree-cooling mode and a cooling mode.

FIG. 4 is a graph illustrating temperature versus time for an airconditioning system utilizing only the cooling mode.

FIG. 5 is a graph illustrating temperature versus time for an airconditioning system utilizing the free cooling determination stepaccording to the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

The present disclosure is directed to an air conditioning system havinga cooling mode and a free cooling mode. More specifically, the presentdisclosure is directed to methods and systems for operating an airconditioning system having a free cooling mode and a cooling mode.

Referring to the drawings and in particular to FIGS. 1 and 2, exemplaryembodiments of an air conditioning system 10 operating in cooling modeand in free cooling mode are shown and generally referred to byreference numeral 10.

Air conditioning system 10 includes a compressor 12, a first valve 14, afirst temperature sensor 16, a condenser 18, a refrigerant pump 20, asecond valve 22, an expansion valve 24, a second temperature sensor 26,an evaporator 28, a controller 30, a third valve 32, a refrigerant 34,and a working fluid 36.

Air conditioning system 10 in cooling mode utilizes compressor 12 topump refrigerant 34 from evaporator 28 to condenser 18. However, airconditioning system 10 in free-cooling mode utilizes a refrigerant pump20 to pump refrigerant throughout the system. Whereas air conditioningsystem 10 in cooling mode does not utilize refrigerant pump 20 duringoperation, air conditioning system 10 in free cooling mode does notutilize compressor 12 during operation.

Referring to FIG. 1, air conditioning system 10 operating in coolingmode operates in a known manner. Specifically, controller 30 is inelectrical communication with third valve 32 so that third valve 32 isadjusted to be in position so that refrigerant 34 can flow fromevaporator 28 to compressor. Controller 30 turns on compressor 12.Controller 30 turns on at least one fan in condenser 18 so that ambientair flows through the condenser. If air conditioning system 10 wasoperating in free cooling mode previously, controller 30 turns offrefrigerant pump 20 and refrigerant 34 flows from condenser 18 throughsecond valve 22 to expansion valve 24, thereby bypassing the refrigerantpump. Compressor 12 compresses refrigerant 34 which flows through firstvalve 14 to condenser 18 wherein there is a heat exchange between therefrigerant and ambient outside air and the refrigerant begins to cool.In one embodiment of the present disclosure, first valve 14 is a checkvalve. First temperature sensor 16 measures the temperature of theambient outside air. Condenser 18 contains a fan that is used to bringoutside ambient air into contact with refrigerant 34 so that heat fromthe refrigerant is transferred to the ambient air. Refrigerant 34 thenpasses through second valve 22, bypassing refrigerant pump 20, toexpansion valve 24. In an embodiment of the present disclosure, secondvalve 22 is a check-valve. When expansion valve 24 is opened, compressedrefrigerant 34 passes through to evaporator 28. Evaporator 28 isconfigured such that working fluid 36 flows through the evaporatorenabling a heat exchange between refrigerant 34 and the working fluid.Second temperature sensor 26 measures the temperature of working fluid36 exiting evaporator 28. From evaporator 28, working fluid 36 flowsthrough third valve 32 to compressor 12. In one embodiment of thepresent disclosure, third valve 32 is a three-way valve. For purposes ofthe present disclosure, it is contemplated that working fluid 36 may beany known type suitable for allowing heat exchange between refrigerant34 and the working fluid. For example, working fluid 36 may be eitherwater or air.

Referring now to FIG. 2, air conditioning system 10 operating in freecooling mode is shown. When entering free cooling mode, controller 30 isin electrical communication with various elements of air conditioningsystem 10 placing each of them in proper configuration such that the airconditioning system can operate in free cooling mode. For example,controller 30 turns off compressor 12 and adjusts third valve 32 so thatrefrigerant 34 flows from evaporator 28 to condenser 18, therebybypassing compressor 12. Additionally, controller 30 turns on at leastone fan in condenser 18 so that ambient air flows through the condenser.Controller 30 also turns on refrigerant pump 20 so that refrigerant 34flows continuously from condenser 18 to the refrigerant pump. Secondvalve 22 is a passive check valve. This valve allows fluid circulationfrom condenser 18 to expansion valve 24 and bans fluid circulation inthe other way, from expansion valve 24 to condenser 18. The mainfunctionality of second valve 22 is to prevent refrigerant 34 fromflowing back to the inlet of refrigerant pump 20, when air conditioningsystem 10 is operating in free cooling mode. Refrigerant pump 20 pumpsrefrigerant 34 from condenser 18 through expansion valve 24 toevaporator 28 wherein there is a heat transfer from the refrigerant toworking fluid 36 is the same manner as discussed above in the coolingmode. Second thermostat 26 measures the temperature of working fluid 36exiting evaporator 28. Refrigerant 34 having a higher temperature thanoutside ambient air, then flows through third valve 32, bypassingcompressor 12, to evaporator 28 as a result of natural refrigerantmigration.

Referring to the FIG. 3, an exemplary embodiment of a method ofoperating an air conditioning system 10 having a cooling mode and a freecooling mode is shown and generally referred to by reference numeral 50.Method 50 includes a free cooling conditions determining step 54 acomparing difference to a pre-determined value step 66, an availablefree cooling capacity step 68, and a free cooling conditions check step74.

Air conditioning unit 10 is either stopped or running in cooling mode52. Advantageously, free cooling condition determination step 54determines whether present conditions are sufficient to operate airconditioning system 10 in free cooling mode rather than in cooling mode,thereby optimizing the utilization of the free cooling mode.

In free cooling conditions determination step 54, the circulation ofworking fluid is activated 56 so that the working fluid flows in througha first opening in evaporator 28 and exits through a second opening.Next, a device is used to measure a first temperature of outside ambientair surrounding the exterior of condenser 18. In one embodiment of thepresent disclosure, a first thermostat 16 is used. Next, a device isutilized to measure the temperature of working fluid 36 exitingevaporator 28. In one embodiment of the present disclosure, a secondthermostat 26 is utilized. It should be recognized that any devicecapable of measuring the temperatures of both working fluid 36 and theoutside ambient air may be used. For example, it is foreseen thatsuitable devices may include, but not be limited to, a thermocoupling ora resistance temperature device.

A difference between the first and second temperatures is thencalculated 62 by controller 30. In one embodiment of the presentdisclosure, controller 30 may utilize a software program to calculatethe difference. The calculated difference is then compared to apre-determined value 64 and a determination is made as to whether thedifference is greater than or equal to the predetermined value orwhether the difference is less than the predetermined value 66. If thedifference is less than the pre-determined value, cooling mode remainson (if air conditioning system 10 was already in cooling mode) orcooling mode will be turned on if the air conditioning system wasstopped. In one embodiment of the present disclosure, the pre-determinedvalue is about six degrees Celsius. If, however, the difference isgreater than or equal to the pre-determined value, there is a systemcheck as to whether the available free cooling capacity is enough 68 tooperate the system in the free cooling mode. If there is sufficientcapacity, air conditioning system 10 switches into free cooling mode 70.When air conditioning system 10 switches into free cooling mode, the airconditioning system operates as shown in FIG. 2. When air conditioningsystem 10 is running in free cooling mode 72, the system performs acontinuous check to see if free cooling conditions are maintained 74.The conditions continuously being monitored include measuring the firsttemperature of outside ambient air, measuring the second temperature ofworking fluid 36 exiting evaporator 28, calculating the differencebetween the first and second temperatures, and comparing the differenceto a pre-determined value.

Air conditioning stem 10 will remain in free cooling mode until step 74determines that present conditions no longer are sufficient. At suchtime, air conditioning system 10 switches into cooling mode 76 andoperates as shown in FIG. 1.

Referring now to FIGS. 4 and 5, graphs are shown wherein time in hoursis plotted on the X-axis and temperature in degrees Celsius is plottedon the Y-axis. Whereas FIG. 5 illustrates an air conditioning systemutilizing the pre-free cooling step according to the present disclosure,the air conditioning system of FIG. 4 does not utilize the pre-freecooling step. In both graphs, a water loop with an initial temperatureof 44 degrees Celsius is brought to a final temperature of 8 degreesCelsius. In FIG. 4, the air conditioning system runs in cooling mode forsix hours in order to bring the temperature of the water loop to 8degrees Celsius. The energy required to do so is 1080 kW/hrs. In FIG. 5,however, the air conditioning system having the pre-free cooling step,operates in free-cooling mode for six hours. Subsequently, the systemoperates in cooling mode for two additional hours. The energy requiredto operate the air conditioning system of FIG. 5 is 468 kW/hrs.Advantageously, it is seen that there is an approximately 57% reductionin the energy usage associated with the cooling system equipped with thepre-free cooling step as contemplated by the present disclosure.

It should also be noted that the terms “first”, “second”, “third”,“upper”, “lower”, and the like may be used herein to modify variouselements. These modifiers do not imply a spatial, sequential, orhierarchical order to the modified elements unless specifically stated.

While the present disclosure has been described with reference to one ormore exemplary embodiments, it will be understood by those skilled inthe art that various changes may be made and equivalents may besubstituted for elements thereof without departing from the scope of thepresent disclosure. In addition, many modifications may be made to adapta particular situation or material to the teachings of the disclosurewithout departing from the scope thereof. Therefore, it is intended thatthe present disclosure not be limited to the particular embodiment(s)disclosed as the best mode contemplated, but that the disclosure willinclude all embodiments falling within the scope of the appended claims.

1. A method of controlling an air conditioning system having a coolingmode and a free-cooling mode, comprising: circulating a working fluidthrough an evaporator of the air conditioning system; measuring a firsttemperature of ambient outside air; measuring a second temperature ofsaid working fluid exiting said evaporator; calculating a differencebetween said first and second temperatures; comparing said difference toa predetermined value; operating the air conditioning system in thefree-cooling mode if said difference is greater than or equal to saidpredetermined value; and operating the air conditioning system in thecooling mode if said difference is less than said predetermined value.2. The method of claim 1, wherein said first temperature of ambientoutside air is measured proximate to a condenser of the air conditioningsystem.
 3. The method of claim 1, wherein measuring said firsttemperature comprises controlling a first temperature sensor todetermine said first temperature and measuring said second temperaturecomprises controlling a second temperature sensor to determine saidsecond temperature.
 4. The method of claim 1, wherein said calculatingstep is performed by a software program.
 5. The method of claim 1,wherein said predetermined value is about six degrees celsius.
 6. Themethod of claim 1, wherein said comparing step is performed duringoperation of the air conditioning system in the cooling mode.
 7. Themethod of claim 1, wherein said comparing step is performed when the airconditioning system is not operating in either the cooling or freecooling modes.
 8. An air conditioning system having a free cooling modeand a cooling mode, comprising: a condenser; a first temperature sensorfor measuring a first temperature of ambient outside air; an evaporatorin separate fluid communication with a working fluid and a refrigerant;an expansion valve being located before said evaporator; a secondtemperature sensor for measuring a second temperature of the workingfluid as the working fluid exits said evaporator; a refrigerant pump forpumping refrigerant from said condenser through an expansion valve tosaid evaporator when the air conditioning system is in the free coolingmode; a second valve for fluidly connecting said condenser to saidexpansion valve when the air conditioning system is in the cooling mode,said second valve for fluidly connecting said condenser to saidrefrigerant pump when the air conditioning system is in the free coolingmode; a compressor for compressing the refrigerant when the airconditioning system is in the cooling mode; a third valve for fluidlyconnecting said evaporator to said condenser when the air conditioningsystem is in the free cooling mode, said third valve for fluidlyconnecting said evaporator to said condenser when the air conditioningsystem is in the cooling mode; and a controller for calculating adifference between said first and second temperatures, said devicecomparing said difference to a predetermined value, said controlleradjusting positions of said first and second valves, turning on saidcompressor, and turning off said refrigerant pump when said differenceis equal to or greater than said predetermined value, said controllerturning off said compressor, turning on said refrigerant pump, andadjusting positions of said second and third valves when said differenceis less than said predetermined value.
 9. The air conditioning system ofclaim 8, wherein said third valve is a three way valve.
 10. The airconditioning system of claim 8, wherein said second valve is acheck-valve.
 11. The air conditioning system of claim 8, wherein saidworking fluid is water.
 12. The air conditioning system of claim 5,wherein said working fluid is air.